Add library tags to allow Dartium to run the crypto tests.

tests/lib/crypto/hmac_sha256_test.dart

Index: tests/lib/crypto/hmac_sha256_test.dart
diff --git a/tests/lib/crypto/hmac_sha256_test.dart b/tests/lib/crypto/hmac_sha256_test.dart
index 59aa65609304922d0cc3345d0c575148fbbe6667..ef0dd2191615ac0ff6fc5f5d2668dcb4f6672f82 100644
--- a/tests/lib/crypto/hmac_sha256_test.dart
+++ b/tests/lib/crypto/hmac_sha256_test.dart
@@ -2,6 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// Library tag to allow the test to run on Dartium.
+#library('hmac_sha256_test');
+
 // TODO(ager): Replace with "dart:crypto" when ready.
 #import("../../../lib/crypto/crypto.dart");